1. Field of the Invention
The present invention pertains to an apparatus and method of stimulating the vestibular system of a patient to provide a therapeutic benefit, and, in particular, to an apparatus and method in which the portions of the labyrinth associated with the labyrinthine sense and/or the nerves associated therewith are stimulated to perform at least one of the following functions: augment or control a patient""s respiratory function, open the patient""s airway, induce or promote sleep, counteract vertigo, or a combination of these functions.
2. Description of the Related Art
There are numerous techniques for providing respiratory assistance to a patient suffering from a respiratory disorder and/or dysfunction. For example, it is known to provide mechanical ventilatory assistance by delivering a flow of breathing gas to the patient""s airway via a ventilator. This mechanical ventilation method of assisting the patient""s respiratory effort has numerous disadvantages that are well documented. For example, the patient interface device, such as a tracheal tube, intubation tube and nasal/oral mask, can be difficult to place within or on the patient, may cause long-term problems in the patient, and/or may not be tolerated by the patient. In addition, because the mechanical ventilator replaces, either partially or completely, the respiratory effort of the patient, the patient may have difficulty being weaned off of the ventilator, especially if the patient has been using a ventilator for an extended period of time.
It is also known to provide ventilatory assistance to a patient by directly stimulating the patient""s phrenic nerve, thereby causing the diaphragm to contract. It is also known to provide this so called xe2x80x9celectroventilationxe2x80x9d technique by placing electrodes on the chest of the patient to innervate the diaphragm or chest muscles directly. See, e.g., U.S. Pat. No. 4,827,935 to Geddes et al. entitled, xe2x80x9cDemand Electroventilator.xe2x80x9d However, these conventional electroventilation techniques are relatively ineffective at imitating the natural respiratory function of the patient, because, in a normal patient, each respiratory effort involves a complex interaction of nerve and muscle stimulation that includes more tissues than just the phrenic nerve and diaphragm. Conventional electroventilation techniques target individual muscles or, at best, muscle groups, not the overall neural-muscular systems that cooperate to produce a normal respiratory cycle.
There are also numerous techniques for maintaining airway patency and/or patient ventilation to treat sleep apnea syndrome. For example, a common technique for treating obstructive sleep apnea (OSA) is to provide the patient with a continuous positive airway pressure (CPAP) or a bi-level pressure that varies depending on whether the patient is in the inspiratory or expiratory phase of the respiratory cycle. The supply of gas to the patient provides a pneumatic splint for the portion of the airway that would otherwise collapse. It is also known to treat central sleep apnea (CSA) using a system similar to a non-invasive ventilator. Preferably, the CSA treatment system detects whether the patient has stopped breathing for a period of time that exceeds a predetermined threshold time period and provides ventilatory assistance if this occurs. These techniques for treating sleep apnea syndrome have disadvantages similar to those associated with providing ventilatory assistance to the patient; namely, some patients have difficulty tolerating the patient interface device. In addition, some patients have difficulty and/or are uncomfortable breathing against the flow of gas being delivered to their airway. Also, because these systems are used while the patient sleeps, they must be kept as quite as possible so as not to arouse the user or the user""s sleep partner.
It is also known to treat OSA by electrically stimulating the musculature in the neck area associated with the upper airway. Relaxation of these muscles during sleep is believed to be a contributing, if not a primary, factor on the occurrence of OSA for many sufferers. One conventional method of electrically stimulating the muscles in the upper airway involves placing an electrode in direct contact with a surface of the patient and passing a current through the surface tissues to stimulate the underlying muscles. For example, an intraoral appliance has been developed that applies an electrical current within the oral cavity to induce contraction of the genioglossus muscle, thereby helping to maintain airway patency. Another known electrical stimulation appliance applies electrical energy to the exterior surface of the patient""s neck below the chin to induce contraction of the underlying upper airway muscles.
Electromuscular stimulation using surface mounted electrodes creates relatively large current densities at the site of the electrodes. Because these current densities are disposed at the surface of the patient, which also typically contains a relatively large number of nerve endings, such electrical stimulation devices might, in some cases, cause unpleasant sensations, possibly arousing the user from sleep. In addition, some patients may not be comfortable wearing an electrical stimulation appliance either on their neck or in their mouth while they sleep.
It is also known to apply electrical stimulation directly to the nerves and/or muscles of the upper airway via electrodes implanted in the patient to induce tension in the muscles of the upper airway, thereby preventing them from collapsing during sleep. As with stimulating the phrenic nerve to induce respiration, these conventional neural-muscular electrical stimulation techniques are relatively ineffective at imitating the natural upper airway muscle contraction function that takes place during normal breathing. Normal breathing involves a complex interaction of nerve and/or muscle stimulation that is precisely timed and is provided at precise stimulation levels so as to prevent airway collapse. Direct invasive, stimulation of the nerves and/or muscles associated with the upper airway targets one nerve/muscle specifically, and, therefore, does not reproduce the overall neuromuscular function of a normal human that is involved in maintaining airway patency during normal breathing. In addition, direct invasive stimulation of the nerves and/or muscles associated with the upper airway is considered to be relatively invasive medical procedure, and, therefore, may not be favored by a large number of patient""s and/or caregivers.
It is also known to treat sleep apnea syndrome through surgical removal of tissues in the upper airway. In addition, pharmacological solutions have also been pursued, at least with respect to the treatment of central sleep apnea. However, neither of these therapies is successful in all cases. Surgical removal of tissue is invasive, introduces a potential for complications, the long term effects are not known, and is only marginally successful. Pharmacological therapy has been, in general, less than satisfactory, and side effects are frequent.
There are many patients that suffer from sleeping disorders in addition to or other than sleep apnea syndrome. For example, many people have difficulty falling asleep. Although the specific pathological reasons why some people have difficulty falling asleep are not believed to be known, many phramacological solutions exist for assisting a person to fall asleep. However, such medications, which are essentially relaxants, may not be appropriate for some people, due to undesirable, known, or unknown drug interactions, for example, and, therefore, are disfavored by some patients and/or caregivers. In addition, these medications may produce undesirable side effects, such as excessive drowsiness. More seriously, these medications may be contraindicated, and, therefore, a health risk.
It is also known that physically rocking the patient can be helpful in inducing sleep. To this end, beds with mechanical rocking mechanisms have been developed. It can be appreciated, however, that the rocking motion may not be tolerated by the patient""s bed partner. In addition, providing a bed that can rock an adult requires relatively costly, mechanically complicated, and potentially noisy rocking mechanisms to move the bed in the desired rocking direction. In addition, such rocking beds are typically cumbersome, aesthetically displeasing and not practical in many homes.
Although not related to respiration or sleep, another disjunction of interest with respect to the present invention is vertigo and/or dizziness, which are disorders in which the sufferer has the sensation that they or their surroundings are whirling. These disorders may be induced by pathological reasons or from the physical movement of the user, such as spinning in a disorienting fashion. Vertigo, for example, may also be the result of an inner ear disorder that effects the patient""s balance system. Depending on the underlying cause, treatment of these disorders include physical therapy, cranial manipulation, surgery, and pharmacological intervention. However, some causes of vertigo and/or dizziness have no cure or treatment. Furthermore, the existing physical therapies, cranial manipulation treatments, and surgeries are time consuming, may be only moderately effective, or are only effective for specific types of diseases. Pharmacological treatments can produce undesirable side effects and may not provide immediate relief.
Accordingly, it is an object of the present invention to provide a system that performs one or more of the following: augment or control a patient""s respiratory function, open the patient""s airway, induce sleep, and/or counteract vertigo that overcomes the shortcomings of conventional treatment techniques. This general object is achieved according to principles of the present invention by providing a vestibular stimulation system that stimulates at least a portion of the labyrinth associated with the labyrinthine sense and/or at least one of the nerves in the inner ear associated with the labyrinthine sense, such as the vestibular nerve and the branch nerves associated therewith. The general configuration for a vestibular stimulation system that accomplishes this object includes a stimulation element that stimulates the targeted tissue, a stimulation power supply and control system that provides and controls the application of stimulation energy to the targeted tissue via the stimulation device, and, in some applications, an input device, such as sensor, for providing input data to the control system so that the control system can determine when and how to apply stimulation energy to the patient via the stimulation element. Configurations for the stimulation system that performs the above identified physiological functions are described briefly below.
Augmenting or controlling a patient""s natural respiratory function is accomplished by stimulating the vestibular nerve and/or one or more nerve branches associated with the vestibular nerve, either directly or indirectly, so as to induce a neural transmission in the vestibular nerve. Because of the interaction between the vestibular nerve and the nerves associated with respiration, such as the phrenic, hypoglossal, and recurrent laryngeal nerves, stimulation induced in the vestibular nerve induces stimulation in the nerves associated with respiration to cause or assist the patient in breathing. By inducing a neural transmission in the vestibular nerve, the vestibular stimulation system can be used to control one or more parameters associated with the patient""s respiration, such as set the start of inspiration, the duration and/or the force of the respiratory effort. For a patient that has compromised respiratory effort, stimulating the vestibular system can be used to assist the patient""s ventilation. If the patient is breathing on their own, but not at an adequate level, stimulating the vestibular system can augment the patient""s natural respiratory function to increase the patient""s respiratory effort. In one embodiment, the present invention contemplates using at least one sensor and a control algorithm or algorithms to synchronize triggering of the vestibular stimulation with the patient""s respiratory cycle. However, the present invention also contemplates providing a time varying stimulation energy to at least a portion of the vestibular system irrespective of the patient""s respiratory cycle. In which case, the patient will synchronize his or her respiratory cycle with this stimulation cycle.
Because stimulation of the vestibular nerve elicits stimulation in the hypoglossal, and recurrent laryngeal nerves, stimulating the vestibular system can also be used to maintain airway patency to treat OSA and upper airway resistance syndrome. Preferably, a sensor detects the patient""s respiratory cycle, such as by monitoring respiration, and the control system applies stimulation to the vestibular system at an appropriate time, duration, and pattern during the respiratory cycle to maintain the patency of the patient""s airway.
Inducing or augmenting sleep is accomplished by rhythmically stimulating the vestibular system, such as the semicircular canal, saccule, utrical and/or ampullae, or the nerve branches associated with these structures, to produce a uniform rocking sensation in the patient. For example, locations on one or more of the semicircular canal(s), saccules, and/or utricles can be stimulated so as to cause a back and forth flow of the fluid in the semicircular canal to create the rocking sensation. This artificially created rocking sensation, like the actual rocking provided by a physically rocking the patient""s bed, helps the patient relax and eventually fall asleep, as well as promotes sleep once the patient has fallen asleep.
Countering vertigo and/or dizziness is accomplished by stimulating the vestibular system in a manner to as to mask out the signals from the vestibular system that would otherwise be interpreted by the brain as a spinning sensation. Preferably, a sensor detects the motion of the patient and/or the unusual activity from the nerves in the inner ear and causes the vestibular stimulation system of the present invention to compensate for this motion and/or unusual neural activity by stimulating the vestibular system in such a manner so as to mask out the signals indicative of spinning and/or the unusual neural signals. Thus, stimulating the vestibular system only takes place when the signals from the vestibular system would be interpreted by the brain as a spinning sensation and/or when the signals from the vestibular system are not normal, which, if not treated, may cause the patient to experience vertigo.
It is yet another object of the present invention to provide a method of augmenting or controlling a patient""s respiratory function, opening the patient""s airway, inducing sleep, and/or counteracting vertigo that does not suffer from the disadvantages associated with conventional techniques for accomplishing these functions. This object is achieved by providing a method that includes providing stimulation to the receptors of the labyrinth associated with the labyrinthine sense and/or the nerves associated with such receptors, including the vestibular nerve and its branches.
For the method of augmenting or controlling a patient""s respiratory function and opening the patient""s airway, this process, in one embodiment of the present invention, includes sensing the condition of the patient, such as his or her respiratory cycle, and synchronizing the stimulation with the inspiratory phase in the case of augmenting the respiratory function. In another embodiment, a time varying stimulation energy is applied to at least a portion of the vestibular system irrespective of the patient""s respiratory cycle, with the patient naturally synchronizing himself or herself to this stimulation cycle. In addition, for opening the patient""s airway, the method can include determining when conditions of the patient suggest that airway closing or cessation of breathing will occur and only provide vestibular stimulation if such conditions are present. For example, the stimulation system can detect when the patient is asleep, lying down, ceases breathing, or snores and begin the stimulation therapy only when one or more such conditions exist.
For the method of inducing or promoting sleep, this stimulation process can include applying stimulation to vestibular system, such as one or more of the semicircular canals, ampullae, saccule and/or utricle, so as to produce a rocking sensation in the patient. In addition, this method can include sensing when the patient is in a preferred body position, such as supine, and/or sensing whether the patient is asleep or awake so that stimulation to produce the rocking sensation is only initiated if the patient is supine and awake, for example. This method can also include providing the stimulation for a set duration, such as a predetermined period of time, following initiation of the stimulation therapy so that the stimulation is applied to put the patient to sleep, but discontinues some time later, preferably once the patient has fallen asleep, much the same way a sleep timer on a radio or television functions to turn of the appliance after a set period of time. Of course, the stimulation process can also continue throughout the sleep duration because the rocking sensation is believed to promote a restful sleep for the patient even after the patient has fallen asleep.
For the method of counteracting vertigo, the vestibular stimulation process includes applying stimulation to the vestibular system in such a manner so as to mask out the signals from the semicircular canals that would otherwise be interpreted by the brain as a spinning sensation. In addition, this method can include sensing the motion of the patient so that the masking stimulation is only applied if the patient is actually in motion.
These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.